Present technology spark ignition engines have the problem of lower efficiency at part load. The loss of efficiency is caused by: loss due to throttling of the intake mixture; slow combustion due to lower density of the throttled mixture; excessive heat loss to the combustion chamber walls and energy wasted in disassociation reactions during combustion.
In addition to low efficiency at part load, present technology engines are troubled by exhaust gas emission problems. Emission of unburned hydrocarbons results from choking when cold starting and from flame quenching at the cylinder walls. Emission of nitrogen oxides results from excessive combustion temperatures.
It is known in the art to overcome some of these problems by exhaust gas recirculation (EGR) and a number of patents have issued which are directed to EGR systems and methods of operating internal combustion engines. Exemplary of such patents are:
Virk et al U.S. Pat. No. 4,265,721 PA1 Resler, Jr. U.S. Pat. No. 4,135,481 PA1 Hattori U.S. Pat. No. 4,119,071 PA1 Gagliardi U.S. Pat. No. 4,011,846 PA1 Might U.S. Pat. No. 4,060,061 PA1 Blaser U.S. Pat. No. 4,060,059 PA1 Villela U.S. Pat. No. 3,905,344 PA1 Dahlstrom U.S. Pat. No. 3,799,130 PA1 Saiki U.S. Pat. No. 4,194,475
While EGR systems are helpful in lowering pollution in internal combustion engines, Indicated Specific Fuel Consumption (ISFC) is also lowered when combustion rates are fast enough.